(Biol 211) Chapter 2: The Chemical Context Of Life

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INQUIRY: What creates "Devil's Garden" in the rain forest?

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organisms are composed of what?

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matter

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Matter:

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anything that takes up space and has mass

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matter is made up of what?

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elements

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elements:

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a substance that cannot be broken down to other substances by chemical reactions.

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Compound:

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a substance consisting of two or more different elements combined in a fixed ratio.

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which elements make up 96% of living matter?

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- carbon
- oxygen
- hydrogen
- nitrogen

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trace elements:

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those elements required by an organism in only minute quantities.

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Naturally Occurring Elements in the Human Body

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atom:

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the smallest unit of matter that still retains the properties of an element.

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what subatomic particles make up the atom?

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- neutrons
- protons (+)
- electrons (-)

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Atomic Nucleus:

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is in the center of an atom and consists of protons and neutrons.

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atomic number:

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tells us the number of protons and electrons in an neutral atom

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mass number:

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= # of protons + # of neutrons

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Isotopes:

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the different atomic forms of an element

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radioactive isotope:

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an isotope in which the nucleus decays spontaneously, giving off particles and energy.

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RESEARCH METHOD: Radioactive Tracers:

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Energy:

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the capacity to cause change (by doing work)

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Potential Energy:

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the energy that matter possesses because of its location or structure.

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Energy levels of an atom's electrons

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Electrons are found in different ____________________

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electron shells

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When electrons absorbs energy what happens?

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it moves to a shell farther out from the nucleus.

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What happens when an electron loses energy?

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it "falls back" to a shell closer to the nucleus, the lost of energy is usually released to the environment as heat.

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valence electrons:

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outer electrons

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valence shell:

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outermost electron shell

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Inert =

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chemically unreactive

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when are atoms chemically reactive?

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when they have incomplete valence shells.

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orbital:

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the 3D space where an electron is found 90% of the time.

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no more than ____ electrons occupy a single orbital/

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2

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Electron orbitals

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Chemical Bonds:

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attractions holding together atoms

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covalent bond:

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the sharing of a pair of valence electrons by two atoms.

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molecule:

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two or more atoms held together by covalent bonds.

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Formation of a covalent bond.

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single covalent bond:

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a pair of shared electrons

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structural formula:

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represents both atoms and bonds

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molecular formula:

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indicates simply that the molecule consist a certain amount of atoms.

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Covalent bonding in four molecules:

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bonding capacity (valence):

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usually equals the number of unpaired electrons required to complete the atom's outermost (valence) shell.

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Electronegativity:

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the more electronegative an atom, the more strongly it pulls shared electrons toward itself.

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nonpolar covalent bond:

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a bond in which the electrons are shared equally

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poplar covalent bond:

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the electrons of the bonds are not shared equally.

- vary in their polarity, depending on the relative electronegativity.

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Polar covalent bonds in a water molecule.

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Ionic bond:

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when two atoms are so unequal in their attraction for valence electrons that the more electronegative atom strips an electron completely away from its partner.

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Electron transfer and ionic bonding

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Ion:

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a charged atom

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cation:

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a positive charged ion.

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anion:

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a negatively charged ion.

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ionic compounds:

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- aka: salts
- compounds formed by ionic bonds.

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What is one of the strongest bonds in organisms?

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covalent bonds

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which certain type of weak chemical bonds are important in organisms?

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- ionic bonds
- hydrogen bonds.

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Hydrogen bond:

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forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom.

- usually pairs w/ O, N in living cells.

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Van der Waals interactions:

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are weak and occur only when atoms and molecules are very close together.

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Molecular shapes due to hybrid orbitals.

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Why is molecule shape crucial in biology?

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because it determines how biological molecules recognize and respond to one another with specificity.

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Endorphins:

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signal molecules made by the pituitary gland that bind to the receptors, relieving pain and producing euphoria during times of stress, such as intense exercise.

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Chemical Reactions

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making and breaking of chemical bonds, leading to changes in the composition of matter.

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Equation for photosynthesis:

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1. In the term trace elements, the modifier trace means?
a. the element is required in vary small amounts
b. the element can be used as a label to trace atoms through an organism's metabolism
c. the element is vary rare on earth
d. the element enhances health but is not essential for the organism's long-term survival.
e. the element passes rapidly through the organism.

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a. the element is required in vary small amounts

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B

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B

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C

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5. The reactivity of an atom arises from:
a. the average distance of the outermost electron shell from the nucleus
b. the existence of unpaired electrons in the valence shell
c. the sum of the potential energies of all the electrons shells
d. the potential energy of the valence shell.
e. the energy differences between the s and p orbitals.

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b. the existence of unpaired electrons in the valance shell.

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6. Which statement is true of all atoms that are anions?
a. the atom has more electrons than protons
b. the atom has more protons than electrons.
c. the atom has fewer protons than does a neutral atom of the same element
d. the atom has more neurons than protons.
e. the net charge is 1-

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a. the atom has more electrons than protons.

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B

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8. Which of the following statements correctly describe any chemical reaction that has reached equilibrium?
a. the concentrations of products and reactants are equal.
b. the rates of the forward and reverse reactions are equal.
c. both forward and reverse reactions have halted.
d. the reaction is now irreversible.
e. no reactants remain.

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b. the rates of the forward and reverse reactions are equal.